When adharma predominates, O Krishna, the women of the family become corrupt. Women tending to be immoral, O Varshneya (Krishna, a descendant of the Vrishni-clan), admixture of varṇas (predominant qualities in a clan) follows.
Kurukshetra war and this dialogue transpired over 5100 years ago, in the social order prevailing at the time. India had hundreds of kings, each having his ambition to conquer the neighbouring rulers and become an emperor, considered to be an adorable adventure!
In the frequent internecine wars, countless kshatriya men used to die, leaving their women far outnumber the men folk, resulting in grave social imbalance and its undesirable consequences.
Kshatriya women used to court inter-caste alliances, often leading to confusion and disorder. It led to the disadvantage of not being able to adhere to their hallowed customs, practices and rituals, inviting traditional disorder, cultural mixture and abuse. Arjuna feels by slaying millions in the impending war, he would be guilty of causing such a social anarchy!